1. Field of the Invention
The present invention relates to an electronic component mounted member in which an electronic component and a circuit board are joined via an electrically conductive adhesive, in the field of mounting electronic components, and to an electronic component mounted member and a repair method thereof permitting improved repair of the component.
2. Description of Related Art
With an increasing attention to environmental issues recently, lead in a solder alloy has begun to be regulated in the field of electronics mounting. Accordingly, there has been an urgent demand for a joining technique for mounting the electronic components using no lead. As the lead-free mounting technique, in general, a lead-free solder and an electrically conductive adhesive can be considered. Because of expected advantages such as flexibility of a joining portion and a lower mounting temperature, the electrically conductive adhesive has attracted more attention.
Generally, the conventional electrically conductive adhesive is formed by dispersing an electrically conductive filler into a resin-based adhesive component. After a terminal of an electronic component and that of a circuit board are connected via the electrically conductive adhesive, the resin is cured, thereby maintaining a conduction of the connected portions by a contact of the electrically conductive fillers. Thus, since the connected portions are adhered to each other by the resin, there are advantages in that it is possible to respond flexibly to heat and deformation due to an external force and it is less likely to generate cracks in the connected portions compared with the solder, where the connected portions are adhered by an alloy. Consequently, the electrically conductive adhesive is expected as an alternative material to the solder.
However, in the conventional electronic component mounted member, once the electrically conductive adhesive is cured in a manufacturing process of the electronic component, it becomes difficult to remove, in other words, to repair the electronic component. This sometimes serves as an obstacle to the practical use of the electrically conductive adhesive. More specifically, for the purpose of obtaining a connection strength of the component, a thermosetting epoxy binder resin often is used for a binder resin of the electrically conductive adhesive. In this case, since the electronic component is removed forcibly by twisting, even after the component is removed, the electrically conductive adhesive remains on a substrate electrode. In an alternative case, there also are problems that the substrate electrode is peeled off from a substrate base material, or neighboring components are damaged.
In addition, some electrically conductive adhesives using thermoplastic binder resins are just becoming commercially-available as an electrically conductive adhesive that is capable of repair. However, such electrically conductive adhesives do not have a sufficient connection strength, and are, therefore, insufficient for a material for mounting electronic components. Also, although a mixture of the thermoplastic binder resin and the thermosetting binder resin has a better connection strength than the electrically conductive adhesive of the thermoplastic binder resin alone, the binder resin forms a lump and remains on a surface of the substrate electrode, so that, after the removal of the electronic component, a mounting work of a replacement electronic component becomes complicated.
As described above, in the mounted member of the electronic component and the circuit board via the conventional electrically conductive adhesive, it has been difficult to achieve both excellent repair characteristics and high connection strength of the electronic component.
With the foregoing conventional problems in mind, in a mounted member of an electronic component and a circuit board via an electrically conductive adhesive instead of solder, it is an object of the present invention to provide an electronic component mounted member and a repair method thereof having high repair characteristics as well as an improved connection strength of the electronic component and the circuit board.
In order to achieve the above-mentioned object, a first electronic component mounted member of the present invention includes a circuit board, an electronic component connected to the circuit board, and an electrically conductive adhesive interposed between the electronic component and the circuit board. In a joining interface of the electrically conductive adhesive and an electrode of the circuit board, an intermediate layer that is formed of a thermoplastic insulating adhesive with a softening temperature of 100xc2x0 C. to 300xc2x0 C. is interposed between the electrically conductive adhesive and the electrode. An electrically conductive filler contained in the electrically conductive adhesive is present partially in the intermediate layer, thus allowing an electrical conduction between the electrically conductive adhesive and the electrode of the circuit board.
Next, a second electronic component mounted member of the present invention includes a circuit board, an electronic component connected to the circuit board, and an electrically conductive adhesive interposed between the electronic component and the circuit board. In a joining interface of the electrically conductive adhesive and an electrode of the circuit board, an intermediate layer that is formed of a thermoplastic insulating adhesive with a softening temperature of 100xc2x0 C. to 300xc2x0 C. and contains an electrically conductive expandable particle is interposed between the electrically conductive adhesive and the electrode. The electrically conductive expandable particle allows an electrical conduction between the electrically conductive adhesive and the electrode of the circuit board.
Furthermore, a repair method of an electronic component mounted member of the present invention includes using the mounted member including a circuit board and an electronic component connected to the circuit board, and when a repair is necessary, heating a portion of the intermediate layer corresponding to the electronic component to be repaired so as to raise a temperature of this portion to at least a melting point of the thermoplastic insulating adhesive, thereby melting the thermoplastic insulating adhesive, and removing the electronic component with this state maintained.